Apparatus for ultraviolet light treatment in a controlled atmosphere

ABSTRACT

Apparatus which permits treatment of products with ultraviolet light in a controlled atmosphere comprises an inner chamber positioned within an outer chamber, the workpiece to be treated passing through the inner chamber. The outer chamber has a means for supplying ultraviolet light in the upper surface of a second or inner chamber whereby ultraviolet light may be radiated in the inner or second chamber. The apparatus may also contain means for carrying the product to be treated, as well as cooling means at either end of the path of treatment.

Elite ttes Patent 1191 Qoleman *Feh. 5, 1974 [54] APPARATUS FOR 1' 1 '1VHOLET LIGHT 3,676,673 7/1972 Coleman 250/49.5 T E TM IN A CQNTROLLED1,969,606 8/1934 Hall 73/150 3,224,266 12/1965 Klippert.... 73/150ATMOSPHERE 2,575,426 11/1951 Parnell 250/52 X [75] Inventor: George E.Coieman, Elmhurst, 111. 2,845,541 7/1958 Berry et al.... 250/522,887,584 5 1959 N d 250 49.5 73 Assignee: PPG industries, 111e,Pittsburgh, Pa. I Notice; The portion of the term f thi PrimaryExaminer-William F. Lindquist patent b q ent to July 1 l, 1989,Attorney, Agent, or Firm-George D. Morris has been disclaimed.

22 Filed: Sept. 8, 1972 [57] S CT Apparatus which permits treatment ofproducts with [21] Appl. No.. 287,400 ultraviolet light in a controlledatmosphere comprises an inner chamber positioned within an outerchamber, [52] 11.8. C1 250/453, 250/432, 250/455, h w rkpiece to bereated passing through the inner 250/492 chamber. The outer chamber hasa means for supply- [51] Int. C1. 11011 37/20 ng l r i l light n h upp rrf of a second. r '[58] Field of Search... 73/150; ll8/49.1, 49.5, 50.1,inner chamber whereby ultraviolet light may be radi- 118/620; 250/42,49.5 TE, 51, 52 ated, in the inner or second chamber. The apparatus mayalso contain means for carrying the product to be [56] Reierences Citedtreated, as well as cooling means at either end of the UNITED STATESPATENTS P of treatment- 2,876,187 3/1959 Wolinski 250/42 X 11 :1 3Drawing Figures 7 l .c f 3 f P 2 1 11/ 5 '5 I 1 15 5 9 5 L a j 3 M/ pf/1 12 L 2 Q L J3 "Q Q} PATENTEU FEB 5 I974 SHEEF 1 BF 2 ll APPARATUS FORULTRAVHOLET LIGHT TREATMENT IN A CONTROLLED ATMOSPHERE BACKGROUND OF THElNVENTlON The ultraviolet light treatment of materials to effect curing,sterilization, etc., is known in the art, and processes involvingultraviolet light are becoming of increasing importance. The applicationand curing of coatings is one area in which radiation with ultravioletlight provides numerous advantages. Irradiation processes are carriedout by treating ultraviolet light sensitive materials to light, at leastpart of which has a wavelength in the ultraviolet region.

The use of ultraviolet light in treating various materials is carriedout by exposing appropriately sensitive materials to light, at leastpart of which has a wavelength in the ultraviolet region. Theultraviolet region is usually considered to extend from about 4,000 A.down to as low as 40 A., although for practical purposes the regionbelow about 2,000 A. is not ordinarily significant. While sunlightincludes wavelengths in the ultraviolet region, as received it haslittle or no light at wavelengths much below 3,000 A. due to absorptionby the atmosphere. Thus, for useful processes it is necessary to use anultraviolet lamp.

Several types of lamps are used to produce ultraviolet light. Mercurylamps, in which an electric discharge is passed through mercury vapor,are the most common, but others include metal halide lamps, luminescentor fluorescent lamps, etc. The so-called Sunlamps can also be employed.

It has been found that the efficiency of ultraviolet light in treatingmaterials in many cases depends upon the environment of the materialbeing treated. For example, many materials are more or less sensitive toultraviolet light, depending upon the atmosphere in which they arelocated. The presence of certain levels of oxygen in the atmosphere isoften a determining factor in both the rate of the desired reaction andthe quality of the finished product. Other factors involve hazards suchas the possibility of fire or explosion and the production of ozoneduring the treatment process.

It is, therefore, often desirable to carry out treatment withultraviolet light in a controlled atmosphere in which the level ofoxygen can be maintained within desired limits. While this is relativelyeasily carried out in a closed system, most processes cannot beeconomically performed in closed apparatus and heretofore it has notbeen possible to provide efficient control of the atmosphere surroundinga workpiece in a process wherein the products treated are continuouslyor intermittently moving.

One proposal for providing an inert atmosphere, suggested for use in aprocess involving electron beam irradiation, is described in U.S. Pat.No. 2,887,584. The apparatus as described therein comprises a chamberopen at the bottom into which the product to be irradiated is passedwhile attempting to maintain a relatively inert atmosphere inside thechamber by use of a lighterthan-air inert gas to displace the airtherein. The apparatus as described in the said patent is quite limitedin the extent to which oxygen can be excluded from the path of theproduct to be irradiated, and for this reason does not appear to havebeen successfully utilized.

The apparatus of the present invention comprises:

A. a first chamber having at least one ultraviolet lamp in a surfacethereof,

18. a second chamber positioned within the first chamber and defining areservoir between the chambers,

C. the second chamber having spaced inlet and outlet openingsestablishing a path of travel for a workpiece and said second chambercontaining means for the passage of ultraviolet light to the secondchamber in the upper surface of the second chamber and said first andsecond chambers substantially completely enclosing said path of travelbetween said inlet and outlet openings, and

D. means for introducing gas into the path of travel of the workpiece.

The present invention provides apparatus for treating products withultraviolet light in an atmosphere in which the level of oxygen or anyother gaseous component can be controlled within quite rigid limits. Forexample, where it is desired to exclude oxygen to the extent possible,the present apparatus can easily attain oxygen levels in the path oftravel of a workpiece as low as parts per million or lower, even whereworkpieces are being continuously irradiated and thus are continuouslymoving through the apparatus.

DESCRIPTION OF THE DRAWlNGS in the drawings: FIG. l is a perspectiveview of an apparatus comprising one embodiment of the invention.

H6. 2 is a longitudinal section through the apparatus Separating thelamps are reflectors S which are cooled by cooling lines 6 which contactthe reflectors and contain circulating water from water lines 7 andmanifolds 8. The ultraviolet lamps extend through the top surface ofouter chamber 1 and the bulbs of the lamps are situated with thereflectors in the upper surface 9 of inner chamber 10. The secondchamber 10 is positioned within the first chamber and has openings 11and 11 through which is passing a workpiece 12. Gas distribution tubes113 are positioned in the reservoir between the chambers and areconnected to a gas source (not shown). Also shown is an auxiliary gasinlet 15 at the inlet opening to the second chamber.

in FIG. 2 the first chamber l with the ultraviolet lamps 2 and 3contains within it a second chamber 10 having inlet and outlet openingsll and Ill. The bulbs of the ultraviolet lamps and the reflectors 5extend to the upper surface 9 of chamber 10. Gas inlet tubes 13 extendtransversely through the apparatus and contain a plurality of holestherein for the introduction of gas, the distribution of the gas beingshown in the drawing by arrows. Conveyor rollers 114 which assist inpassing the workpiece are in the lower surface of the second chamber andcooling tubes 16 provide cooling of the bottom surface of the secondchamber in the path of the ultraviolet light. At each of the openings inthe second chamber, a gas distribution tube 15 is provided, alsoextending transversely across the opening and having a plurality ofholes for the passage of gas.

In FIG. 3 the apparatus of FIGS. l and 2 is shown wherein the bulbs forthe ultraviolet lamps and the reflectors do not form part of the surfaceof inner chamber but a window 17 for passing ultraviolet light isprovided at surface 9. Thus, the first chamber l, with the ultravioletlamps 2 and 3 contains within it a second chamber 10 having inlet andoutlet openings M and 11 Ultraviolet light transmitting window 17 in thesecond chamber is in juxtaposition with the ultraviolet lamps 2 and 3and allows the ultraviolet light to travel to the'workpiece 12. Gasinlet tubes 13 extend transversely through the apparatus and contain aplurality of holes therein for the introduction of gas, the distributionof the gas being shown in the drawing by arrows. Conveyor rollers 14 arein the lower surface of the inner chamber and cooling tubes 16 providecooling of the bottom surface of the inner chamber in the path of theultraviolet light. At each of the openings in the inner chamber, a gasdistribution tube 15 is provided, also extending transversely across theopening and having a plurality of holes for the passage of gas.

DESCRIPTION or THE PREFERRED EMBODIMENTS The first or outer chamber ofthe apparatus can be of any suitable size or shape depending upon thenature of the product or workpiece to be treated. it is usuallyrectangular in shape with the ultraviolet lamps attached to the insidesurface. The lamps employed can be any of the commercially availablelamps which emit light in the ultraviolet region, preferably one whichemits predominantly in the range of 2,000 A. to 4,000 A. Mercury vaporand metal halide vapor lamps are generally utilized. The distance fromthe lamp to the workpiece is not ordinarily critical within reasonablelimits, and the optimum distance varies with the intensity of theultraviolet light, the nature and size of the material treated, thespeed with which the workpiece is carried through the ultraviolet lightzone, and similar factors. In the apparatus illustrated, the lamps arelocated about 1 to 16 inches from the conveyor. it is not alwaysnecessary that the lamps be within the chamber in which the workpiece istreated. However, where the lamp is located outside the chamber, asuitable window made of a material which transmits ultraviolet light,such as quartz should be used so as to permit the ultraviolet light toimpinge on the desired portion of the path of travel of the productbeing treated.

In some instances, the ultraviolet lamps in the outer chamber can bepart of a common surface with the inner chamber. Such an arrangement hasthe advantage of eliminating windows and thus reduces the loss ofultraviolet light occasioned thereby, but also makes the apparatus lessflexible.

The second or inner chamber is positioned within the first chamber,thereby defining a reservoir between the inner surface of the firstchamber and the outer surface of the second chamber. While it isdesirable that the second chamber be of a size such that the heightabove the surface of the workpiece is minimized, its size is also notcritical. However, the distance the light must travel before meeting thesurface of the workpiece affects the distribution of energy in theproduct treated. The volume of the reservoir thus depends upon the 4number and type of gas inlets, the flow rate of gas, and the overalldimensions of the components of the apparatus.

The second chamber has openings establishing the path of travel for theworkpiece. Ordinarily, these openings are at either end of the secondchamber and the path of travel passes through the chamber and beneaththe path of the ultraviolet light. The area of these inlet and outletopenings should be as low as possible to permit the passage of theworkpieces, and the larger the area of the inlet and outlet, the longerthe path of travel through the second chamber should be. The object isto provide a stable condition inside the second chamber, therebyminimizing differences due to external changes in atmosphere, such ascaused by air movements. The dimensions of the openings can be varieddepending upon size and shape of the workpiece; the shape of the openingcan be regular or irregular as required. Replaceable or moveableopenings of different configurations can be provided if desired.

The apparatus also comprises means for the introduction of gas into thepath of travel of the workpiece. This is usually accomplished byproviding a plurality of gas inlets in the reservoir between thechambers and then providing means for the passage of the gas into thesecond chamber. Where the second chamber contains an opening for thepassage of the ultraviolet light, this can serve as one of or the onlymeans for the gas to enter the second chamber. Alternatively, the gascan be introduced into the second chamber, although this is lessdesirable, or an opening or other passageway can be provided in thesecond chamber at some point other than the point at which theultraviolet light enters the second chamber.

The number and arrangement of inlets for the introduction of gas anddirection of flow of the gas can be varied, and in fact, it has beenfound that different types of processes require different arrangements.Therefore, it is desirable to provide a plurality of such inlets andthat means be provided so that the direction of gas flow can be varied.it is further desirable that these inlets be based at various pointsthroughout the reservoir. Thus, the preferred arrangement is a series ofgas distribution tubes spaced in the reservoir and extendingtransversely through the apparatus, these gas distribution tubes havinga plurality of inlet holes along their length and being rotatable, thuspermitting changing the direction of flow. A manifold connected to a gassource is usually employed to provide a uniform gas pressure to each ofthe gas distribution tubes.

As indicated, the overall size of the apparatus can be varied. Theapparatus can be constructed of any material which is not overlysensitive to ultraviolet light, i.e., which does not substantiallydegrade and become unusable when subjected to the type of lightemployed. Most metals, glass, plastic, etc., can be used. It ispreferred that a noncorrosive material be utilized and stainless steelis the specifically preferred material of construction.

The apparatus can also be provided with certain optional components.Means for conveying the workpiece along the path of travel canbeincluded, these being, for example, rollers located in the lower portionof the second or inner chamber; these can be power-driven if desired. itis also desirable to include cooling means in the area of the secondchamber upon which the ultraviolet light impinges when not entirelyabsorbed by any material being treated. Such cooling means can be tubesfilled with circulating fluid, a block of heatconducting material, awater or other reservoir,'or any other means which permits absorptionand/or transfer of heat.

Other auxiliary equipment which is often desirable include means forintroducing gas at the inlet and outlet; these can be gas distributiontubes similar to those located in the reservoir, placed above theopening with gas flow directed downward, preferably at 45 angle. Stillother optional features include provision for continuously orperiodically analyzing the atmosphere inside the chamber, means forviewing the workpiece, such as cameras, etc., vacuum or other pumps, andthe like.

The apparatus can be varied in structure to meet the needs of specificprocesses in which it is employed. For example, the apparatus can beused in conjunction with more than one source of ultraviolet light byproviding a plurality of lamps as required. For example, both sides of aworkpiece can be exposed, if desired, or a workpiece of complex shapecan be treated from various angles.

In one embodiment of the invention, an apparatus as shown in thedrawings comprises a first or outer chamber 21 inches long. Attached tothe top inner surface are two ultraviolet lamps, each 12 inches long,one a Sylvania mercury vapor lamp rated at 330 watts per inch and theother a Sylvania metal halide seeded mercury vapor lamp rated at 330watts per inch. The lamps are arranged so that either or both can beused at any one time. Each lamp has a polished aluminum reflector, eachreflector having attached a coil through which cooling water iscirculated when the lamps are in operation. The lamps are spaced fromabout 1 inch to 16 inches from the conveyor which passes beneath thelamps and through the chamber, depending upon the spacer employed. Thesecond or inner chamber is 55 inches long, 14 inches wide and 2 inchesdeep. Each of the inlet and outlet openings in the second chamber is 14inches wide by 2 inches high and the upper surface of the second chambercomprising the bulbs of the ultraviolet lamps surrounded by a foraminouspanel. Eight gas distribution tubes positioned above and below thesecond chamber in the reservoir area extend transversely through theapparatus; the tubes are rotatabL and each tube has l hgle per inchthereip each hole being 0.090 incfii diameter. The tubes are connectedto a manifold which is in turn connected to a source of nitrogen. Aconveyor is used to pass the workpiece through the second chamber withthree power-driven rollers in the bottom of the second chamber aiding inthe passage.

The apparatus as described is constructed of stainless steel and canaccommodate workpieces up to about 12 inches wide and about 1 inchthick.

In operation of the above-described apparatus, a total nitrogen flow of60 cubic feet per minute is passed through the manifold and distributedby the gas distribution tubes in the reservoir. A product line iscarried through the second chamber at a rate of about 150 feet perminute. During such operation, the concentration of oxygen in the pathof travel of the workpiece is less than 150 parts per million. Byreducing the speed of travel and/or the size of the product line, theoxygen content can be reduced to below 60 parts per million.

The apparatus can also be used to provide a sustained level of oxygen(or other gas) during operation. This is desirable using some coatingmaterials, for example, and is accomplished by feeding a controlledmixture of oxygen and nitrogen through the gas distribution system. Anadvantage of the use of the apparatus in this manner is that ozone andother gaseous by-products are removed during operation and thus theconcentration of such by-products does not build up to undesirably highlevels. The apparatus can also be operated at reduced pressure, byproviding suitable auxiliary equipment, e.g., pumps, chambers, etc.

According to the provisions of the patent statutes, there are describedabove the invention and what are now considered to be its bestembodiments. However, with the scope of the appended claims, it is to beunderstood that the invention can be practiced otherwise than asspecifically described.

I claim:

l. in an apparatus for treating products with ultraviolet light in acontrolled atmosphere A. a first chamber having at least one ultravioletlamp in a surface thereof,

B. a second chamber positioned within said first chamber and defining areservoir between said 1 chambers,

C. said second chamber having spaced inlet and outlet openings for aworkpiece establishing a path of travel for said workpiece and havingmeans for the passage of ultraviolet light in juxtaposition with saidultraviolet lamp,

D. said first and second chambers substantially com-. pletely enclosingsaid path of travel between said inlet and outlet openings, and

E. means for introducing gas into said path of travel.

2. The apparatus of claim l in which said second chamber extends throughsaid first chamber.

3. The apparatus of claim l in which said means for introducing gascomprises means for introducing gas into said reservoir.

41. The apparatus of claim l in which said means for the passage ofultraviolet light in said second chamber is a window in one surface ofsaid chamber.

5. The apparatus of claim l in which said means for the passage ofultraviolet light in said second chamber is the extension of the lampsso that the bulbs of the lamps form 'part of a surface of said secondchamber.

6. The apparatus of claim l in which cooling means is provided in aportion of the surface of said second chamber.

7. The apparatus of claim 1 in which said means for introducing gascomprises a plurality of gas distribution tubes.

8. The apparatus of claim H in which additional means for theintroduction of gas are provided at the said inlet and outlet openingsin said second chamber.

9. The apparatus of claim 1 in which means for conveying the workpiecealong said path of travel is provided in the lower surface of saidsecond chamber.

16. The apparatus of claim 9 in which said means for conveying theworkpiece comprises rollers.

ill. The apparatus of claim 1 in which said means for the passage ofultraviolet light in said second chamber is an opening in the surface ofsaid chamber.

1. In an apparatus for treating products with ultraviolet light in acontrolled atmosphere A. a first chamber having at least one ultravioletlamp in a surface thereof, B. a second chamber positioned within saidfirst chamber and defining a reservoir between said chambers, C. saidsecond chamber having spaced inlet and outlet openings for a workpieceestablishing a path of travel for said workpiece and having means forthe passage of ultraviolet light in juxtaposition with said ultravioletlamp, D. said first and second chambers substantially completelyenclosing said path of travel between said inlet and outlet openings,and E. means for intRoducing gas into said path of travel.
 2. Theapparatus of claim 1 in which said second chamber extends through saidfirst chamber.
 3. The apparatus of claim 1 in which said means forintroducing gas comprises means for introducing gas into said reservoir.4. The apparatus of claim 1 in which said means for the passage ofultraviolet light in said second chamber is a window in one surface ofsaid chamber.
 5. The apparatus of claim 1 in which said means for thepassage of ultraviolet light in said second chamber is the extension ofthe lamps so that the bulbs of the lamps form part of a surface of saidsecond chamber.
 6. The apparatus of claim 1 in which cooling means isprovided in a portion of the surface of said second chamber.
 7. Theapparatus of claim 1 in which said means for introducing gas comprises aplurality of gas distribution tubes.
 8. The apparatus of claim 1 inwhich additional means for the introduction of gas are provided at thesaid inlet and outlet openings in said second chamber.
 9. The apparatusof claim 1 in which means for conveying the workpiece along said path oftravel is provided in the lower surface of said second chamber.
 10. Theapparatus of claim 9 in which said means for conveying the workpiececomprises rollers.
 11. The apparatus of claim 1 in which said means forthe passage of ultraviolet light in said second chamber is an opening inthe surface of said chamber.